hi dear as all your routine tests and serology are normal i would go for some rare possibilities it can be infectious mononucleosis ,a viral disease - a serology for cytomegalovirus is to be done endocarditis (inflammation of inner layer of heart can be a cause -2d echo is to be done to rule out you have not mentioned your drinking habits ,but as you have grade 2 fatty liver , cirrhosis can also cause moderate spleenomegaly( you should do a FNAC liver if usg is normal to find out cause of grade 2 fatty liver). blood cancers like leukemia can be a cause of it ,investigations should be done to rule out the posibility,especialy hodkins lymphoma is associated with it Metabolic disorders, such as Gaucher s disease and Niemann-Pick disease- are very rare but genetic reading is to be done to rule out this rare cases are rare but they do happen,a thorough investigation is to be done to find out the cause in your case